1. Field of the Invention
The present disclosure relates to the synthesis of linear and hyperbranched polytriazoles by fast and region-selective 1,3-dipolar cycloaddition of organic azides and acetylenes by metal-free thermal methodology.
2. Related Art
The unique molecular structures of polytriazoles render them with novel features, such as for use with respect to photoresist and light emission. There are many publications that disclose linear polytriazoles, which were obtained by Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction (for examples: Helms, B.; Mynar, J. L.; Hawker, C. J.; Fréchet, J. M. J. J. Am. Chem. Soc. 2004, 126, 15020. (b) Englert, B. C.; Bakbak, S.; Bunz. H. F. Macromolecules, 2005, 38, 5868. (c) Binder, W. H.; Kluger, C. Macromolecules, 2004, 37, 9321. (d) Tsarevsky, N. V.; Sumerlin, B. S.; Matyjaszewski K. Macromolecules, 2005, 38, 3558). But when the conditions disclosed conditions are applied for the synthesis of hyperbranched polymers, partially soluble or totally insoluble materials are always obtained (Scheel, A. J.; Komber, H.; Voit, B. I. Macromol. Rapid. Commun. 2004, 25, 1175), which prohibits investigation of the resultant materials and their practical applications.
After Huisgen's comprehensive review in 1984 (Huisgen, R. In 1,3-Dipolar Cycloaddition Chemistry; Padwa, A., Ed.; Wiley: New York, 1984), the research on 1,3-dipolar cycloaddition reactions remained silent until Sharpless and coworkers recognized the potential application and found an efficient method to synthesize the regioselective 1,2,3-triazoles from organic azides and terminal acetylenes by Cu(I) catalysts. (V. V. Rostovtsev, L. G Green, V. V. okin, K. B. Sharpless Angew. Chem. Int. Ed. 2002, 41, 2596; and K. B. Shapless, US 2005/0222427 A1). Due to its high yield and high regioselectivity, they defined this methodology as “Click Chemistry”. This breakthrough aroused tremendous interest among scientists in particular for the construction of bio-conjugated materials and only limited reports have addressed electro-optical macromolecular materials (D. J. V. C. Steenis, O. R. P. David, G. P. F. Strijdonck, J. H. Maarseveen, J. N. H. Reek Chem. Commun. 2005, 4333).
Because of their substantially globular molecular architectures, hyperbranched polymers are envisioned to exhibit novel properties such as low viscosity and high thermal stability and serve as functional materials. Moreover, the synthesis of hyperbranched polymers can be done in a one-pot single-step procedure. Realization of the full potential of hyperbranched polymers calls for the exploration of new, versatile methods for their syntheses,
Schell, et al. reported for the first time hyperbranched polymers constructed by either Cu(I)-catalyzed or thermal 1,3-dipolar cycloadditions of AB2 type monomers (where A represents one azide group and B2 represents two acetylenes, all in one organic molecule; Scheel, A. J.; Komber, H.; Voit, B. I. Macromol. Rapid. Commun. 2004, 25, 1175). This methodology contains some disadvantages, which limit its practical applicability. Soluble hyperbranched polymers can only be obtained when the Cu(I) catalyzed 1,3-dipolar cycloaddition is performed in highly polar solvents (such as DMSO or DMF), which are difficult to remove after polymerization. Another problem is the self-polymerization of this type of monomer when stored for long time under ambient conditions.
Steenis et al. reported the light emission properties of linear polytriazoles prepared by Cu(I)-catalyzed 1,3-dipolar cycloaddition with conjugated diazides and diacetylenes. However, this methodology requires a long reaction time (up to 170 h) and may hamper again its usage when employed in practical applications. Most of the other linear polymers containing 1,2,3-triazole moieties (B. Helms, J. Am. Chem. Soc. 2004, 126, 15020; B. C. Englert, Macromolecules, 2005, 38, 5868; W. H. Binder, Macromolecules, 2004, 37, 9321; N. V. Tsarevsky, Macromolecules, 2005, 38, 3558) are again only soluble in high polar solvents, such as DMF and DMSO, which is very inconvenient for investigations of their properties and further processing.
Wurziger et al. (U.S. Pat. No. 7,009,059) reported the 1,3-dipolar cycloaddition between azides and acetylenes groups of mainly low molecular weight compounds in microreactors. Manzara (U.S. Pat. No. 5,681,904) reported cross-linked polymers. The author adopted 1,3-dipolar cycloaddition between polymers containing azido groups either in the main chain or as pendants and diacetylenic esters or amides. The resulting polymers were insoluble and the inventor did not provide any information of the regioselectivity of the product.
It is known that aroylacetylenes can be cyclotrimerized when refluxed in DMF or in mixtures with other solvents such as toluene for a long time (J. Org. Chem. 2002, 67, 4547). The inventors have abundant experiences on the polycyclotrimeriazation of aroylacetylene monomers (Dong, H. C.; Zheng, R. H.; Lam, J. W.-Y.; Haeussler, M.; Qin, A. J.; Tang, B. Z. Macromolecules, 2005, 38, 6382-6391).
Further, compounds with azido moieties can form active radicals when irradiated with UV light (Bräse, S.; Gel, C.; Knepper, K.; Zimmermann, V. Angew. Chem. Int. Ed. 2005, 44, 5188).